1. Field of the Invention
The present invention relates to a motor drive control system which drives and controls at least one motor which is provided at an axis of a machine tool, industrial machine, robot, etc.
2. Description of the Related Art
In such a motor drive control system, in order to control rotational speed of a motor, alternating-current voltage or alternating current from a commercial alternating current power supply such as a three-phase alternating current power supply is converted once into direct-current voltage or direct current, then the direct-current voltage or the direct current is converted into any frequency alternating-current voltage or alternating current, then the converted alternating-current voltage or the converted alternating current is supplied to the motor. To do this, the motor drive control system is connected to one alternating current/direct current (AC/DC) conversion circuit which converts alternating-current voltage or alternating current to direct-current voltage or direct current and has at least one direct current/alternating current (DC/AC) conversion circuit which converts direct-current voltage or direct current to alternating-current voltage or alternating current and supplies the converted alternating-current voltage or alternating current to the motor.
Conventionally, in order to add a motor which can be driven and controlled by the motor drive control system, a motor drive control system which enables connection of one or more DC/AC conversion devices at the outside of the motor drive control system has been proposed, for example, in Japanese Patent No. 3626152 (JP3626152B). In this case, the DC/AC conversion device converts direct-current voltage or direct current into alternating-current voltage or alternating current and supplies the converted alternating-current voltage or the converted alternating current to the motor which is added to the motor drive control system so as to enable the motor which was added to the motor drive control system to be driven and controlled by the DC/AC conversion device. When a DC/AC conversion device is connected to such a motor drive control system, the AC/DC conversion circuit supplies direct-current voltage or direct current to at least one direct current/alternating current conversion circuit and at least one direct current/alternating current conversion device.
In a conventional motor drive control system which enables connection of a DC/AC conversion device, when one or more DC/AC conversion devices are connected to the motor drive control system, and a motor connected to a DC/AC conversion device is driven, because of large output of the motor connected to the DC/AC conversion device (for example, the output of the motor which is connected to the DC/AC conversion circuit of the motor drive control system), there may be a situation where the total of the outputs of the motors to be driven exceeds power which can be supplied from the AC/DC conversion circuit. Therefore, according to a conventional motor drive control system which enables connection of a DC/AC conversion device, there is a disadvantage of overloading the AC/DC conversion circuit when the total of the outputs of the motors to be driven exceeds power which can be supplied from the AC/DC conversion circuit.